Device for the leak-tight assembly of heat exchangers in nuclear reactors

ABSTRACT

A leak-tight passage is provided for a heat-exchanger shell within an opening formed in the primary vessel wall of a fast reactor. The opening comprises a vertical cylindrical collar surmounted by an annular bell which is rigidly fixed to the heatexchanger shell and shaped so as to constitute in conjunction with the collar an annular space between the cylindrical collar an annular bell which is maintained unprimed by injecting a gas under pressure into this space.

United States Patent Vercasson 1 Jan. 8, 1974 1 DEVICE FOR THELEAK-TIGHT 3,656,543 4/1972 Wolowdiak 176 65 ASSEMBLY or HEAT EXCHANGERS1N g fv 1 s at son NUCLEAR REACTORS 3,507,747 4/1970 Strohmeyer.... [75]Inventor: Michel Vercasson, La Celle-Saint .251 89 6/ 1966 DeightonCloud, France 3,161,570 12/1964 Hammond et al. 176/65 X 3,150,051 9/1964Ammon 176/65 X 1 Assigneel Commissariat a lEnergie qu 3,187,807 6 1965Ammon 165/74 Paris, France 3,511,310 5/1970 Van Loo 165/74 X 2 F d: A 41 7 [2 l "g 9 1 Primary Examiner-Carl D. Quarforth PP 168,924 AssistantExaminer-Roger S. Gaither Attorney-Craig, Antonelli & Hill [30] ForeignApplication Priority Data Aug. 7, 1970 France 70.29197 [57] ABSTRACT Aleak-tight passage is provided for a heat-exchanger [52] U.S. Cl 176/63,176/40, 176/62, hell Within an Opening formed in the primary vessel I1-76/64, 165/74 wall of a fast reactor. The opening comprises a verti-[51] Int. CL... G216 13/02, G210 13/06, F28d 1/06 cal cylindrical collarsurmounted by an annular bell [58] Field of Search 176/65, 62, 40, 63;which is rigidly fixed to the heat-exchanger shell and 165/159, 74shaped so as to constitute in conjunction with the collar an annularspace between the cylindrical collar an [56] References Cited annularbell which is maintained unprimed by inject- UNITED STATES PATENTS ing agas under pressure into this space.

3,498,880 3/1970 Gollion 176/65 X 6 Claims, 2 Drawing Figures 13 113?'l3 7 /4- E l 1L 4 22 i 11 1'. 1 1 1 I 4-; Li.) &

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INVENTOR MICHEL VER AS5 ON BY mq aMtwm; HLQQ ATTORNEYS PATENTED JAN 8I974 SHEEIEUF 2 IN VENTOR MICHEL VERCA ssoN ATTORNEYS 1 DEVICE FOR THELEAK-TIGHT ASSEMBLY OF HEAT EXCHANGERS IN NUCLEAR REACTORS ln fastreactors, the coolant is often liquid sodium by reason of its highheat-transfer coefficients, the low pressure of coolant circuits and thehigh reliability of cooling in all states of reactors.

This fluid circulates in a closed circuit from a primary vesselcontaining the reactor core at the bottom central portion to a mainouter vessel from which the fluid is returned by pumping to the reactorcore and to the primary vessel. The equipment units which are necessaryfor cooling and especially the pumps and intermediate heat exchangerswhich operate in parallel are immersed in the liquid sodium around thereactor core. The shells of the active portion of each heat exchangerextend vertically within the two vessels and the wall penetrations ofthe primary vessel are intended to be leak-tight.

This invention relates to a simple arrangement for the leak-tightassembly of each heat exchanger; this arrangement results in totalleak-tightness while allowing freedom for the radial and axialdisplacements of the heat exchanger which arise especially fromtemperature or pressure variations and permits assembly or disassemblyof the heat exchanger without any need for working within the interiorof the reactor.

The invention is concerned with a device for the leak-tight assembly ofa heat-exchanger shell through an opening of the primary vessel wall ofanuclear reactor, characterized in that the opening comprises a verticalcylindrical collar surmounted by an annular bell which is rigidly fixedto the heatexchanger shell, said bell being shaped so as to constitutein conjunction with the collar an annular spore between the collar andbell which is maintained unprimed by injection of a gas at the topportion.

The gas will preferably be the same as the so-called blanket or covergas which is present above the liquid sodium beneath the shield roof ofthe reactor. This gas is usually argon.

Further characteristic features of the invention will become apparentfrom the description which is given hereinafter, reference being made tothe accompanying drawings which illustrate one non-limitative example ofconstruction of the device contemplated in the foregoing, and in which:

FIG. 1 is a diagrammatic view in transversesectional elevation showing areactor equipped with the device according to the invention;

FIG. 2 is a detailed but diagrammatic viewof the right-hand portion ofFIG. land showing the leak-tight assembly of a heat exchanger with theducts and elements which serve to ensure good operation of the device.

As shown in FIG. 1, the primary vessel 2 of the nuclear reactor and themain vessel 3 are'both filled with liquid sodium 1. The verticalcentrifugal pumps such as the pump 31 suck the liquid sodium from themain vessel 3 through the windows 34 and inject the sodium through aduct 33 into the collector 32; from this collector, the liquid sodiumpasses upwards through the diagrid 35 into the reactor core 30 and isdistributed within the primary vessel 2, then flows into theintermediate heat exchangers 4 so as to return into the main vessel andrepeat the same cycle. The argon blanket is located at 9 above theliquid sodium.

As shown on the right-hand side of F l6. 1, the shell of the activeportion of each heat exchanger 4 extends through the wall which forms aseparation between the primary vessel 2 and the main vessel 3 within theupward conical portion of said wall or skew section 5. The deviceaccording to the invention for providing a leaktight heat-exchangerpenetration is shown in general outline and will now be described indetail together with its ancillary elements, reference being made solelyto FIG. 2.

The opening for the penetration of the heat exchanger 4 through the skewsection is delimited by a vertical cylindrical collar 7; an annular bell8 having a height which is substantially equal to that of the collar hasbeen added to the heat-exchanger shell. The respective transversedimensions of the collar and of the bell are such that, at the time ofassembly, the bell is fitted over the collar in the position shown inthe drawings. An annular space (7, 8) is thus formed around the entireheat exchanger. In order to ensure leaktightness, said space mustnecessarily be continuously unprimed and this result is obtained byinjecting argon under sufficient pressure into the top portion of thespace. Under these conditions, the levels of the sodium within the innerand outer branch of the annular space reproduce respectively the levelsof the liquid sodium within the main vessel and within the primaryvessel with a relative displacement A H in height.

If A P is- 'the pressure difference between the argon contained in thespace (7, 8) and the argon blanket 9, we have in accordance with thebasic theorem of hydrostatics:

AH AP/pg wherein p is the mass per unit volume of the sodium, g is theacceleration of gravity.

It is possible to maintain the levels within the bell at acceptablevalues in all cases of operation of the reactor, namely during normaloperation or during fault conditions, and in particular to prevent anypriming of the space which would divert a part of the flow away from thenormal path which passes through the heat exchangers.

By reason of the fact that the levels within the space cannot bemeasured directly, said levels can be deduced from the levels within thereactor by means of the measurement of AP. The quantity last mentionedwill therefore be employed for the operation of any level-controllingand regulating system.

In order to permit an operational control of this type under theinfluence of AP, the following equipment is accordingly employed:

The value of AP is measured by means of a differential pressuretransducer 15 which is connected respectively to the pressure taps 11 onthe siphon and 10' on the argon blanket 9 beneath the shield roof 22 ofthe reactor; the reference numeral 12 designates the pipe for the supplyand discharge of argon contained in the space between the bell andcollar respectively through the electrovalves 19 and 20.

The supply of argon to the space between the bell and collar ordischarge of argon from this latter is accordingly controlled by adevice 21 which is actuated by the differential pressure transducer 15and causes either opening or closure of one of the electrovalves l9 and20 in accordance with requirements.

The reference numeral 13 designates sodium vapor traps and the numeral14 designates isolating valves;

the cover-gas pressure gauge has the reference 16 and the bell has thereference 17.

It is worthy of note that, under conditions which will be explainedbelow, the discharge valve can be dis pensed with and replaced by acheck valve 18 upstream of the valve 19 in the pipe 12.

Control and regulation of the levels within the bell or the annularspace between the cylindrical collar and annular bell can be carried outby means of the equip ment which has just been described in accordancewith three different methods:

a. Method of the isolated bell Assuming by way of example that thereactor is shut down under conditions of handling of elements, the bellis filled with argon until AP is given a reference value AP the bell isthen isolated by closing the valve 14 of the pipe 12 in order to retaina constant quantity of argon. It is possible to choose AP in such amanner as to ensure that the progressive variation of temperatures, ofpressures and of levels within the reactor during operation of thislatter does not result either in priming of the siphon or in leakage ofargon at the base of the bell. Progressive variation oflevels within thebell is followed continuously by virtue of the measurement of AP and oflevels within the reactor.

As a result of a suitable arrangement of the ducts, a single equipmentunit for measuring and supply (pressure transducers and valves) can beemployed for all heat exchangers (usually six).

b. Method involving maintenance of AP between two reference values Thevalue of AP is maintained between two reference values AP, and AP andoverstepping of these threshold values automatically results in eitheradmission ordischarge of argon into or from the bell through the valves19 or 20. A single equipment unit can also be contemplated.

c. Method involving maintenance of AP above a minimum threshold valueThis method is adopted when it is desirable to have a circulation ofargon in one direction within the external pipes in order to reducedangers of clogging and the problems set by the activity of the argon.

The supply of the bell is carried out through the check valve 18.

In order to prevent any priming of the space between the annular belland cylindrical collar, the value of AP is not permitted to fall belowthe minimum threshold AP which is imposed by the previous method. On theother hand, removal of excess argon is permitted to take place in theform of bubbles at the bottom portion of the bell during temperaturerises.

The disadvantage of the method last mentioned lies in the fact that itentails the need for an equipment unit which is adapted to each heatexchanger.

The device according to the invention thus achieves the desired standardof leak-tightness by pneumatic means. This solution has many advantagesover any mechanical systems which could be devised, viz:

elimination of forged and machined parts of bellowstype compensators,

elimination of contacts, thereby removing the danger of wear andseizure,

elimination of displacement stresses,

reduction of thicknesses and therefore of thermal stresses,

insensitivity to small deformations,

complete removal of leakages of cooling fluid.

What we claim is:

1. In a nuclear reactor with rapid neutrons cooled by circulation of aliquid metal, comprising a principal tank with a vertical axis, and aprimary tank being coaxial with respect to the principal tank andcontaining the core of the reactor, said tanks being filled with theliquid metal topped by a cover ofa neutral gas, the primary tankcomprising a transverse notch equipped with openings for communicationbetween the two tanks, receiving bodies of heat exchangers having avertical axis, being distributed around the core and dipping into theliquid metal, each exchanger comprising at the upper part thereofcontained in the primary tank above the transverse notch inlet orificesfor the liquid metal, and at the lower part thereof in the principaltank below the transverse notch, outlet orifices for said metal, andpumps for circulating the liquid metal discharging from each exchangerand feeding it back into a collector disposed under the core, aregulable sealing device mounted between the primary tank and theprincipal tank in each of the openings of the transverse notch, saiddevice comprising a cylindrical annular collar surrounding the body ofthe exchanger traversing each opening, being integral with the notch andopen at the upper part thereof in the primary tank, an annular bellhaving a height substantially equal to that of the collar and beingintegral with the body of the exchanger, being open at the lower endthereof and outwardly capping and covering said collar and forming anannular space around the entire heat exchanger, and a system forinjecting a neutral gas under pressure into said annular space comprisedbetween the bell and the collar for preventing the direct passage of theliquid metal from the primary tank into the principal tank through saidannular space.

2. A leak-tight assembly device in accordance with claim 1, wherein thegas is the same as the cover gas which is located above a free level ofliquid metal.

3. A device according to claim 2, wherein the cover gas is argon.

4. A device in accordance with claim 1, wherein said device comprises anequipment unit for controlling and regulating the levels of liquid metalwithin the annular space around the entire heat exchanger formed by theannular bell and cylindrical collar and said unit comprises a transducerfor measuring the pressure difference, AP, between the gas in theannular space and the cover gas, said transducer being capable ofselectively initiating according to the values of AP, the operation of avalve for regulating the pressure of the gas confined within the annularspace defined by the collar and bell.

5. A device in accordance with claim 4, wherein the atmosphere of theannular space is isolated by means of a valve after filling with gas at'a pressure corresponding to a reference value AP which is chosen so asto ensure leak-tight operation of the annular space with a constantquantity of gas within the annular space.

6. A device in accordance with claim 4, wherein the operation of thedevice involves regulation between a minimum threshold value AP and amaximum threshold value AP and overstepping of said values causes thetransducer to initiate either admission or discharge of gas into or fromthe annular space.

1. In a nuclear reactor with rapid neutrons cooled by circulation of aliquid metal, comprising a principal tank with a vertical axis, and aprimary tank being coaxial with respect to the principal tank andcontaining the core of the reactor, said tanks being filled with theliquid metal topped by a cover of a neutral gas, the primary tankcomprising a transverse notch equipped with openings for communicationbetween the two tanks, receiving bodies of heat exchangers having avertical axis, being distributed around the core and dipping into theliquid metal, each exchanger comprising at the upper part thereofcontained in the primary tank above the tranSverse notch inlet orificesfor the liquid metal, and at the lower part thereof in the principaltank below the transverse notch, outlet orifices for said metal, andpumps for circulating the liquid metal discharging from each exchangerand feeding it back into a collector disposed under the core, aregulable sealing device mounted between the primary tank and theprincipal tank in each of the openings of the transverse notch, saiddevice comprising a cylindrical annular collar surrounding the body ofthe exchanger traversing each opening, being integral with the notch andopen at the upper part thereof in the primary tank, an annular bellhaving a height substantially equal to that of the collar and beingintegral with the body of the exchanger, being open at the lower endthereof and outwardly capping and covering said collar and forming anannular space around the entire heat exchanger, and a system forinjecting a neutral gas under pressure into said annular space comprisedbetween the bell and the collar for preventing the direct passage of theliquid metal from the primary tank into the principal tank through saidannular space.
 2. A leak-tight assembly device in accordance with claim1, wherein the gas is the same as the cover gas which is located above afree level of liquid metal.
 3. A device according to claim 2, whereinthe cover gas is argon.
 4. A device in accordance with claim 1, whereinsaid device comprises an equipment unit for controlling and regulatingthe levels of liquid metal within the annular space around the entireheat exchanger formed by the annular bell and cylindrical collar andsaid unit comprises a transducer for measuring the pressure difference,Delta P, between the gas in the annular space and the cover gas, saidtransducer being capable of selectively initiating according to thevalues of Delta P, the operation of a valve for regulating the pressureof the gas confined within the annular space defined by the collar andbell.
 5. A device in accordance with claim 4, wherein the atmosphere ofthe annular space is isolated by means of a valve after filling with gasat a pressure corresponding to a reference value Delta P0 which ischosen so as to ensure leak-tight operation of the annular space with aconstant quantity of gas within the annular space.
 6. A device inaccordance with claim 4, wherein the operation of the device involvesregulation between a minimum threshold value Delta P1 and a maximumthreshold value Delta P2 and overstepping of said values causes thetransducer to initiate either admission or discharge of gas into or fromthe annular space.